The present invention relates generally to the manufacture of detergents and more particularly to a method for producing a laundry detergent bar and to an intermediate product for use in the manufacture of a laundry detergent bar.
Laundry detergents, including laundry detergent bars, contain a surface active ingredient which is usually produced by reacting a liquid organic material with sulfur trioxide to produce a sulfonic or sulfuric acid of the liquid organic material and then neutralizing the acid to produce a salt of the sulfonic acid or sulfuric acid. That salt is the surface active ingredient in the laundry detergent.
Typical liquid organic materials used in the production of surface active ingredients for laundry detergents are alkyl benzene and C.sub.8-20 fatty alcohols or ethoxylated derivatives of said fatty alcohols. When alkyl benzene is reacted with SO.sub.3, the reaction is called sulfonation and the reaction product is alkyl benzene sulfonic acid; and when the latter is neutralized (e.g., with sodium hydroxide), the resulting salt is sodium alkyl benzene sulfonate.
When a C.sub.8-20 fatty alcohol or an ethoxylated derivative thereof is reacted with SO.sub.3, the reaction is called sulfation, and the reaction product is a sulfuric acid of the fatty alcohol or ethoxylated derivative thereof; and when the sulfuric acid is neutralized (e.g., with sodium hydroxide) the resulting reaction product is a sodium salt of the sulfuric acid. As used herein, the term "fatty alcohol sulfuric acids" includes both true fatty alcohol sulfuric acids and ethoxylated fatty alcohol sulfuric acids, unless the context indicates otherwise.
A sulfonation or sulfation process may require a digestion period to complete the reaction to the extent desired, although for sulfation, the digestion period, if there is one, is usually relatively short if not absent.
The surface active ingredient is only one of the ingredients of a laundry detergent bar. Other ingredients, both solid and liquid, are mixed with the surface active ingredient, and this mixture is then subjected to other processing steps, conventional in the manufacture of laundry detergent bars, such as refining, extruding, cutting, conditioning and stamping.
It is desirable that the bar manufacturing process be conducted independently of the reaction process for producing the sulfonic or fatty acid sulfuric acid, so as to insure continuous, uninterrupted production of one processing system should the other be shut down due to mechanical difficulties. In order to uncouple these two processes, it must be possible to store the reaction product resulting from the sulfonation or sulfation process. When the reaction product is sulfonic acid, there is no problem with storage because the sulfonic acid does not degrade or break down during storage. Alkyl benzene sulfonic acid, in the concentration normally utilized for making laundry detergent bars, can be readily pumped from the sulfonation processing line to a storage container where the sulfonic acid can be held until it is needed in the bar manufacturing process at which time the sulfonic acid is neutralized and the resulting sulfonate is then fed into the mixer for the bar manufacturing process.
In contrast, fatty alcohol sulfuric acid or the sulfuric acid of ethoxylated derivatives of the fatty alcohol are not stable during storage and break down to common sulfuric acid (H.sub.2 SO.sub.4) and "oil." In order to provide a stable, storable product, these fatty alcohol sulfuric acids must be neutralized, and they should be neutralized with sufficient immediacy following the completion of the sulfation reaction to prevent said breakdown or other problems which arise when they are not immediately neutralized.
When the above-described fatty alcohol sulfuric acids are neutralized in the conventional manner with sodium hydroxide, an aqueous slurry is formed. The viscosity of this neutralized slurry, and the ease with which this slurry can be stored and handled depend upon the solids content or concentration of this slurry, i.e., the amount of surface active ingredient in the slurry.
When the laundry detergent bar contains neutralized fatty alcohol sulfuric acid as the surface active ingredient, it is important that the bar contain a percentage of that surface active ingredient corresponding to the percentage of surface active ingredient which is present when the detergent bar contains alkyl benzene sulfonate as the surface active ingredient. A typical alkyl benzene sulfonate content for laundry detergent bars is in the range 26-32 wt. %, and a typical water content for such bars is in the range 3-12 wt. %. The amount of neutralized fatty alcohol sulfuric acid required to replace that amount of alkyl benzene sulfonate, at the water content indicated, requires a neutralized slurry concentration in the range of about 71-90%. At this concentration, the solids content and viscosity of the neutralized slurry are so high as to render the neutralized slurry very difficult to handle from a pumping and storage standpoint. Such a viscous slurry requires heated, agitated storage containers with heat-traced conduits and pumps capable of handling high solids content slurries. This equipment is relatively expensive.
Because alkyl benzene is derived from petroleum whereas fatty alcohols or the ethoxylated derivatives of fatty alcohols are not, there are many instances where it is desirable to employ, in a laundry detergent bar, surface active ingredients manufactured from fatty alcohols or their ethoxylated derivatives rather than from alkyl benzene.